Method of forming clay articles around a compressible mandrel

ABSTRACT

A hollow ceramic form is made by providing a disposable armature of suitable size and shape and placing wet pliable clay around the armature. The armature or mandrel is comprised of an inner layer of compressible material such as foam rubber and an outer initially rigid layer that softens after it has been in contact with the wet clay form for a short period of time. This compressible mandrel permits the clay body to shrink without cracking while acting as a support until the clay body is selfsupporting. After allowing the clay to partially dry to the extent it is self-supporting, the armature is disposed of by combustion or dissolution and the form is then completely dried by conventional drying and shrinking techniques.

United States Patent n:

Patel et a1.

[ METHOD OF FORMING CLAY ARTICLES AROUND A COMPRESSIBLE MANDREL [76] Inventors: Narendra Patel, 50 74 N. Berkeley; Bernard J. Roberts, 214 Roosevelt Rd., both of Whitefish Bay, Wis.

[22] Filed: Sept. 17, 1971 [21] Appl. No.: 181,555

Related U.S. Application Data [63] Continuation-impart of Ser. No. 883,137, Dec. 8,

1969, abandoned.

[56] References Cited UNITED STATES. PATENTS 1,563,529 12/1925 Satterlee 264/D1G. 44

2,665,469 1/1954 Hymel 264/59 llll 3,758,653

[ 1 Sept. 11, 19,73

Primary Examiner-John H. Miller A!t0rney-J0hn W. Michael 57 1 ABSTRACT A hollow ceramic form is made by providing a disposable armature of suitable size and shape and placing wet pliable clay around the armature. The armature or mandrel is comprised of an inner layer of compressible material such as foam rubber and an outer initially rigid layer that softens after it has been in contact with the wet clay form for a short period of time. This compressible mandrel permits the clay body to shrink without cracking while acting as a support until the clay body is self-supporting. After allowing the clay topartially dry to the extent it is self-supporting, the armature is disposed of by combustion or dissolution and the form is then completely dried by conventional drying and shrinking techniques.

3 Claims, 12 Drawing Figures Patented Sept. 11, 1973 2 Sheets-Sheet 1 lawn/Zr; Wamrzara pals! %rnarw @Zvrla Patented Sept. 11, 1973 2 Sheets-Sheet 2 Jflwmons Warm: dm 4 14 1 METHOD OF FORMING CLAY ARTICLES AROUND A COMPRESSIBLE MANDREL REFERENCE TO COPENDING APPLICATION This application is a continuation-in-part of our application Ser. No. 883,137 filed Dec. 8, 1969, and now abandoned.

BACKGROUND OF INVENTION A principal problem in the manufacturing or production of ceramic forms is that clay, upon drying, shrinks approximately 6 percent to percent from the wet clay form to the final fired completed form. The shrink- I age caused by improper drying techniques results in undesirable warping and/or cracking of the ceramic form. To minimize this problem, methods have been proposed which provide for hollow ceramic pieces even in those cases where only the exterior shape is important.

Prior proposals include adding coils of clay on top of one another or the hollowing out of a piece of semihard clay. These proposals obviously are cumbersome and, in addition, prevent exactness as to the shape and size of theinterior. Alternative proposals call'for the making of a model which is then made into amold, and the ceramic piece is then cast from the mold by piecing the clay into the mold or by pouring the wet clay into the mold as the mold is rotated. The ceramic is then removed and dried in the conventional manner. All of the foregoing calls for a detailed and lengthy step-by-step processing which adds greatly to the expense of the finished product.

SUMMARY 0F INVENTION In making small, hollowceramic pieces, this invention calls for the provision of a soluble armature which has been formed into a desired shape by various techniques such as carving, or extruding etc. Wet and pliable clay is then placed around the armature forming the exterior into a desirable shape. The wet clay is then allowed to dry to a point where it is self-supporting at which point the armature isdissolved by a suitable solvent. Upon dissolution of the armature, the remaining clay form is then dried and cured in a conventional manner.

In making hollow pieces of ceramic forms of significant size wherein shrinking and cracking-during the preliminarydrying'processfis a major problem, this invention contemplates amethod which'provid'es for a combustible armature which I is both compressible and water absorbing. Such an armature is provided by a multi-layered armaturehaving an inner core, a middle core which is compressible, and an outer core or shell which is initially rigid and yet water-soluble. After the armature is formed into a desired shape, wet and pliable clay is placed around it. The combination is then sealed from the atmosphere and allowed tobegin drying internally. Water passes from the wetclay to the rigid outer shell and in so doing softens the outer shell as it absorbs the water. The water in the clay softensthe outer shell and allows the clay to shrink against the compressible middle layer without cracking. When the BRIEF DESCRIPTION or THE DRAWINGS FIG. 1 is a perspective view of one armature proposed by this invention;

FIG. 2 is a cross section of the armature after wet clay has been applied; FIG. 3 is the same view as FIG. 2 with the armature in a state of partialdissolution;

FIG. 4 is a perspective view of the final clay form proposed by this invention;

FIG. 5 is a perspective view of the inner core portion of an alternative armature proposed by this invention;

FIG. 6 is a perspective cutaway view showing the inner and intermediate core of an alternative armature;

FIG.- 7 is a perspective cutaway view showing the intermediate core and a portion of the shell of an alternative armature;

FIG 8 isa perspective cutaway showing the intermediate and'outer shellportio'ns of an alternative armature; A

FIG. 9 is a perspective cutaway showing an alternativearr'n'ature with wet, pliable clay formed around it;

FIG. 10 is a perspective view of an intermediate portion of an alternative portion proposed by this invention;

FIG. 11 is a perspective view showing the outer shell wrapped around the armature of FIG. 10; and

FIG. 12 is a perspective view showing the wet, pliable clay formed around the armature of FIG. 11.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to the drawings in detail, FIGS. 1-4 show one embodiment contemplating an armature 10 comprised of a soluble material which lends itself readily to carving or extruding. Expanded polystyrene is very suitable for thispurpose and can be shapedto'a high degree of accuracy. Armature; l0 is formed into the shape desired for the interior of the finished piece of pottery l2-shown in FIG. 4 to be an artistically shaped I pitcher. After the armature is formed, wet and pliable firing destroys the armature since its entire content is combustible.

clay is appliedaroundthe armature,-the exterior portion being smoothed or roughed off to provide the desired finish or design. The combination of armature 10 and applied wetclay 14 is then allowed to partially dry at room temperature until the clay is selfsupporting. j

After the clay has dried sufficiently to support itself, a suitable solvent l6is brought into contact with the armature thereby dissolving it. Upon dissolution, the piece of pottery. is allowed to completely dry by conventional methods such as slow exposure to air, and then is kiln fired. Gasoline or lacquer thinner has been found to be a suitable solvent when the armature is comprised of expanded polystyrene. The above embodiment lends itself to the formationof small pieces of pottery since, although expanded polystyrene is basically incompressible, the amount of shrinkage of the piece duringthe-preliminary drying stage is not sufficient to cause. serious cracking. Caution should be taken, of course, not to allow excess preliminary drymg.

An alternative method is shown in FIGS. 5-9 comprising a disposable armature which is entirely combustible rather than soluble. The preferred armature 20 is comprised of several layers of combustible material beginning with an inner core 22 which is preferably solid such as light wood; an intermediate layer 24 which is compressible such as foam rubber; and an outer shell 26 which is initially rigid and yet water absorbent. A suitable outer shell is one comprised of papier-mache 28 covered by a layer of burlap 30 sized with wheat paste. Sized or plain papier-mache may be used alone as may burlap but the working time and results are generally better with the combination.

The hard outer shell of the armature provides support for the pounding and texturing of the wet clay during the forming operation as well as during drying. The flexible intermediate layer 24 may vary in thickness depending on the shrinkage of the clay used or the size of 20 the final ceramic form. The function of this intermediate layer is that as the outer shell absorbs moisture or water from the clay, it will become pliable and yield as the clay shrinks. The compressibility of the intermediate layer permits this shrinkage without cracking whether the clay dries uniformly or unevenly while still providing support for the heavy, wet clay. The water is absorbed by the water-absorbing outer shell, and it partially removes the moisture from the clay and thus enables the clay to begin to support itself by becoming harder. Upon preliminary drying to the point that the clay is self-supporting and dry enough for kiln firing, the entire combination of clay and armature is kiln fired with the armature burning away as the clay is formed into a ceramic form.

It has been found that this method works especially well if the clay and armature are covered with a plastic bag or other suitable sealing means to prevent atmospheric drying during the preliminary stage as this forces all the mositure absoprtion to act through the outer shell which provides for a more efficient shrinkage relief.

The method just described is particularly useful where large clay objects are desired such as planters, vases, sculptures, portrait armatures, figure armatures human, animal, etc. Complex commercial objects like sewer elbows and connections are also easy to make by this method since an exact armature would easilybe produced and reproduced by a manufactured form.

FIGS. 10-12 show an alternative of the method just described. In those instances where the size of the ceramic form is of moderate size, it has been found unnecessary to provide an inner solid rigid core 22 for the armature as described in the previous embodiment. Instead it is sufficient simply to provide a flexible inner core 34 such as foam rubber or sponge, etc. with an outer core 36 similar to or the same as outer shell 26 described above. In all other aspects, the entire method is the same as described with respect to FIGS. 5-9.

Thus, the embodiments calling for a combustible armature permit an armature made entirely of organic material with or without a rigid inner core which armature dries with the clay and is burned away in the kiln firing of the final ceramic form.

We claim: 1. The method of making ceramic forms comprising the steps of providing a disposable armature of suitable size and shape, forming wet and pliable clay around said armature whereby'the interior of the shaped clay assume the exterior shape of said armature while the exterior of the clay is shaped into suitable form, said armature being comprised of inner and outer layers, said inner layer being comprised of a compressible material permitting the clay to shrink without cracking,

said outer layer being comprised of a material different than .the material of said inner layer and sized with wheat paste to be initially rigid to withstand the working of the clay and to become water absorbent to partiallyv remove moisture from the clay to enable the clay to begin to be self-supporting while said outer layer becomes soft enough, because of the absorption of water, to yield to allow the clay to shrink as the inner core compresses,

allowing the clay to partially dry until self-supporting,

applying means to dispose of the armature from within .the self supporting clay.

2. Method according to claim 1 wherein the armature and applied clay are enclosed in sealing means to initially prevent atmospheric drying of the clay until said outer layer has become water absorbent and has partially removed moisture from the clay and has softened to insure shrinkage relief as the clay shrinks against the compressible inner core.

3. The method of claim 1 in which the armature is provided with an innermost rigid core.

s n: a: a: 

1. The method of making ceramic forms comprising the steps of providing a disposable armature of suitable size and shape, forming wet and pliable clay around said armature whereby the interior of the shaped clay assume the exterior shape of said armature while the exterior of the clay is shaped into suitable form, said armature being comprised of inner and outer layers, said inner layer being comprised of a compressible material permitting the clay to shrink without cracking, said outer layer being comprised of a material different than the material of said inner layer and sized with wheat paste to be initially rigid to withstand the working of the clay and to become water absorbent to partially remove moisture from the clay to enable the clay to begin to be self-supporting while said outer layer becomes soft enough, because of the aBsorption of water, to yield to allow the clay to shrink as the inner core compresses, allowing the clay to partially dry until self-supporting, applying means to dispose of the armature from within the self supporting clay.
 2. Method according to claim 1 wherein the armature and applied clay are enclosed in sealing means to initially prevent atmospheric drying of the clay until said outer layer has become water absorbent and has partially removed moisture from the clay and has softened to insure shrinkage relief as the clay shrinks against the compressible inner core.
 3. The method of claim 1 in which the armature is provided with an innermost rigid core. 